[Code of Federal Regulations]

[Title 47, Volume 5]

[Revised as of October 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 47CFR87.141]



[Page 198-199]

 

                       TITLE 47--TELECOMMUNICATION

 

        CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION (CONTINUED)

 

PART 87_AVIATION SERVICES--Table of Contents

 

                    Subpart D_Technical Requirements

 

Sec.  87.141  Modulation requirements.



    (a) When A3E emission is used, the modulation percentage must not 

exceed 100 percent. This requirement does not apply to emergency locator 

transmitters or survival craft transmitters.

    (b) A double sideband full carrier amplitude modulated 

radiotelephone transmitter with rated carrier power output exceeding 10 

watts must be capable of automatically preventing modulation in excess 

of 100 percent.

    (c) If any licensed radiotelephone transmitter causes harmful 

interference to any authorized radio service because of excessive 

modulation, the Commission will require the use of the transmitter to be 

discontinued until it is rendered capable of automatically preventing 

modulation in excess of 100 percent.

    (d) Single sideband transmitters must be able to operate in the 

following modes:



------------------------------------------------------------------------

                                        Level N(dB) of the carrier with

             Carrier mode                respect to peak envelope power

------------------------------------------------------------------------

Full carrier (H3E)...................  ON-6.

Suppressed carrier (J3E).............  Aircraft stations N<-26;

                                       Aeronautical stations N<-40.

------------------------------------------------------------------------



    (e) Each frequency modulated transmitter operating in the band 72.0-

76.0 MHz must have a modulation limiter.

    (f) Each frequency modulated transmitter equipped with a modulation 

limiter must have a low pass filter between the modulation limiter and 

the modulated stage. At audio frequencies between 3 kHz and 15 kHz, the 

filter must have an attenuation greater than the attenuation at 1 kHz by 

at least 40 log10 (f/3) db where ``f'' is the frequency in 

kilohertz. Above 15 kHz, the attenuation must be at least 28 db greater 

than the attenuation at 1 kHz.

    (g) Except that symmetric side bands are not required, the 

modulation characteristics for ELTs must be in accordance with 

specifications contained in the Federal Aviation Administration (FAA) 

Technical Standard Order (TSO) Document TSO-C91a titled ``Emergency 

Locator Transmitter (ELT) Equipment'' dated April 29, 1985. TSO-C91a is 

incorporated by reference in accordance with 5 U.S.C. 552(a). TSO-C91a 

may be obtained from the Department of Transportation, Federal Aviation 

Administration, Office of Airworthiness, 800 Independence Avenue SW., 

Washington DC 20591.



[[Page 199]]



    (h) ELTs must use A3X emission and may use A3E or NON emissions on 

an optional basis while transmitting. Each transmission of a synthesized 

or recorded voice message from an ELT must be preceded by the words 

``this is a recording''; transmission of A3E or NON emission must not 

exceed 90 seconds; and any transmission of A3E or NON emissions must be 

followed by at least three minutes of A3X emission.

    (i) ELTs manufactured on or after October 1, 1988, must have a 

clearly defined carrier frequency distinct from the modulation sidebands 

for the mandatory emission, A3X, and, if used, the A3E or NON emissions. 

On 121.500 MHz at least thirty per cent of the total power emitted 

during any transmission cycle with or without modulation must be 

contained within plus or minus 30 Hz of the carrier frequency. On 

243.000 MHz at least thirty percent of the total power emitted during 

any transmission cycle with or without modulation must be contained 

within plus or minus 60 Hz of the carrier frequency. Additionally, if 

the type of emission is changed during transmission, the carrier 

frequency must not shift more than plus or minus 30 Hz on 121.500 MHz 

and not more than plus or minus 60Hz on 243.000 MHz. The long term 

stability of the carrier frequency must comply with the requirements in 

Sec.  87.133 of this part.

    (j) Transmitters used at Aircraft earth stations must employ BPSK 

for transmission rates up to and including 2400 bits per second, and 

QPSK for higher rates.



[53 FR 28940, Aug. 1, 1988, as amended at 54 FR 11721, Mar. 22, 1989; 56 

FR 11518, Mar. 19, 1991; 57 FR 45749, Oct. 5, 1992]